Minimally invasive devices, such as catheters, are often employed for medical procedures, including those involving cardiac ablation. In a particular situation, an ablation procedure may involve creating a series of inter-connecting or otherwise continuous lesions in order to electrically isolate tissue believed to be the source of an arrhythmia. Such lesions may be created using a variety of different energy transmission modalities, such as cryogenic freezing.
Catheters or devices using cryogenic cooling may be used to lower the temperature of tissue, such as cardiac wall tissue, to an extent such that signal generation or conduction temporarily ceases and allows one to map or confirm that the catheter is positioned at a particular lesion or arrhythmogenic site. Cryogenic catheters may also operate at lower temperatures for ablation treatment, e.g., to cool the tissue to a level at which freezing destroys the viability of the tissue, and, in the case of cardiac tissue, permanently removes it as a signal generating or signal conducting locus.
Whether or not a particular treatment is successful may depend greatly on the qualities or characteristics of the lesion, such as its depth, uniformity, location, or the like. For example, for a given cardiac arrhythmia, a particular lesion depth and shape may be required to effectively obstruct the unwanted signal transmission through the problematic tissue region. Current cryogenic ablation devices create lesions by transfer of heat from the target tissue to either a balloon filled with cryogenic fluid or a substantially linear catheter tip. By using pull wires to deflect the distal end of the ablation device and/or regulating the inflation rate of the balloon, the size and shape of the treatment end of the ablation device may be imprecisely modified to create a desired shape of the ablation element for the particular lesion to be formed. However, such modifications are done during a particular procedure, not before, and require the skill of the surgeon using the ablation device to determine how to modify the treatment end of the ablation to create the desired lesion. Furthermore, such ablation devices have fixed ablation elements, whether a distal tip for creation of a focal lesion or balloon for a creation of a circumferential lesion, but not both.
Accordingly, there remains a need for medical devices that have ablation elements that are pre-fabricated to desired shapes to improve lesion formation, minimize error, reduce procedure time, and that are transitionable to different shapes and sizes depending on the type and location of the lesion to be created with minimal skill needed by the surgeon.